The preferred embodiment relates to a control device for a technical processing plant, in particular an industrial processing plant, that can be employed in the technical domain of chemistry, petro-chemistry, gas processing, production of pharmaceuticals, foodstuffs, cellulose, paper, glass, steel, cement and the like. In an industrial processing plant technical processes are running wherein continuously or discontinuously fluid streams relating to a main process are acted upon. For example, in large chemical plants, in pharmaceutical plants, in steel making and cement production, in a waste incineration plant, a foundry, etc. process fluid streams are formed that are to be adjusted according to process and operation depending on certain control variables such as temperature or throughput amount. In industrial processing plants also raw materials may be obtained such as metal from ore. Therein the raw material of a processing routine may itself be the product of a preceding process. Also the production of finished products or the recycling of raw material from waste and garbage falls into the technical domain of process engineering.
A generic control device for a technical processing plant is known from the published patent application DE 1 043 739, in which a stop valve is to be actuated by a pneumatic actuator. Besides the pneumatic actuator the control device has a control valve designed to adjust a process fluid stream. An actuator stem is coupled to a valve stem via a stem connector formed as a sleeve and providing an unalterable coupling between the valve and the actuator stem. At the valve side the sleeve has an internal thread engaging with an external thread at the end section of the valve stem. Two predefined positions can be set by means of the thread coupling between the valve stem and the actuator stem in order to vary the total length of the stem arrangement and provide a different functionality of the stop valve.
A similar, proven control device structure is known from DE 10 2006 061 017 A1, in which the stem connector is a sleeve that is unadjustably connected to the actuator stem via a head-groove-connection while a threaded engagement is present between the valve stem and the end of the sleeve facing the valve stem.
For the known control device it became apparent that after mounting the control valve it is difficult for an operating person that has to check processing procedures of the plant without being very familiar with the control valve to determine how large is the maximum stroke length, i.e. what maximum valve opening the valve member may adopt relative to the valve seat.
In particular when mounting and unmounting of the pneumatic positioning actuator of the control valve is required as a result of a desired change in functionality, in particular when the valve stem is deeply threaded into the stem connector, a relatively large amount of assembly work must often be performed by inexperienced personnel in order to achieve the disengagement of the stem connector from the valve stem.